**3.2 Fermentation kinetics**

**Figure 1** shows the average of the fermentative kinetics evolution of Malvasia musts at 10°C. Skin contact for 6 hours does not influence the development of fermentation (a), no differences were found in terms of fermentation time and velocity between vinifications (**Table 2**). However, in the case of skin-contact for 18 hours (b), there are differences in the time and velocity of fermentation compared to the conventional one. The macerated must concludes its fermentation almost a week before the conventional one. This fact may be related to the YAN content and its high content of nutrients and fermentation activators, which seem to have a strong influence on the process (see **Table 1**).

General composition of wines obtained with skin-contact treatment and conventional way from cv. Malvasia *aromatica* are given in **Table 3**. Wines from skin contact treatments had lower values for total acidity. There was no significant difference for any quality parameter that is in accordance with research published

#### **Figure 1.**

*Fermentative kinetics evolution of Malvasia musts. (a) Assay 1, skin-contact 18 h (M18). (b) Assay 2, skin-contact 6 h (M6).*


*V50: amount of sugar daily transformed when 50% of the sugar content had been used up; Vf: Fermentation velocity (daily sugar % lost).*

#### **Table 2.**

*Influence of skin-contact on fermentation velocity.*


#### **Table 3.**

*General composition of wines obtained with different treatment: Conventional (C) and skin-contact treatment: Assay 1 (A1), 18 h (M18) and assay 2, 6 h (M6).*

studies [22–24]. As explained in point 2.2, the conventional way samples were different from each other, hence the difference in ethanol content.

### **3.3 Influence on aroma compounds**

Varietal aromas from grapes, terpenols and C-13 and those from fermentation were determined. The aromatic compounds have been grouped by aromatic families: terpenols, C13, alcohols, lactones, acids, esters, aldehydes and ketones (**Table 4**). These were 37 aromatic compounds studied from the three processing methods together with an analysis of variance to determine the influence of two maceration times (18 hours and 6 hours) on the total volatile content. In addition, the real contribution of each compound to the aroma of the wine was measured by the corresponding perception thresholds.

**Table 5** shows the odor threshold values (OTH) and their sensory descriptors for those compounds with odor activity values (OAVs) >1, which actively contribute to the aroma of the wines.

In both assays, skin contact treatment increased the total concentration of volatiles in wines compared to the control wine. From the A1, the control and M18 wines contained 303.9 and 413.9 mg/L and from A2, the control and M6 309.9 and 318.1 mg/L of volatiles, respectively. Similar results were found by other authors [6, 28] on different varieties. Also, in a study carried out using a period of contact between the skins and the must of the Narince grape variety resulted in an increase of the aromatic content of the wines subjected to maceration [29].

Higher alcohols were the most abundant family of volatile compounds in the four winemaking processes, contributing more than 90% of the total volatile


*Influence of Skin-Contact Treatment on Aroma Profile of Malvasia* Aromatica *Wines… DOI: http://dx.doi.org/10.5772/intechopen.99216*


*Significance at which means differ as shown by analysis of variance: \* p < 0.05; \*\* p < 0.01; \*\*\* p < 0.001. Ns: not significant; Nd: non detected; Tr: traces.*

### **Table 4.**

*Effect of skin contact on the aroma compound levels of Malvasia* aromatica *wines.*

content analyzed. Higher alcohols, in quantities below 300 mg/L can contribute to improving the aromatic complexity of white wines, however are considered to be a negative factor in terms of aromatic quality when they exceed 400 mg/l [30]. Isobutanol, isoamyl alcohol and 2-phenylethanol were the most abundant in the four wines analyzed. Among the higher alcohols, M18 has increased the levels of 2-phenylethanol being 5.3 (**Table 5**). This compound is related to floral aromas with attributes of roses and is considered to contribute positively to wine aroma [31]. There has been a significant decrease of 1-hexanol y cis-3-hexen-1-ol in M18 wines in comparison to the control. These compounds are related to herbaceous aromas and bitter taste so are unfavorable to wine quality. Skin contact treatment for 18 h resulted in significant increase in the concentration of the esters ethyl 3-hydroxybutyrate and ethyl hexanoate esters, however, the concentrations of ethyl butyrate, isoamyl acetate and hexyl acetate decreased with the maceration time. Esters are very important for the aroma of wine, they are related to fruity aromas [32]. Due to their high OAVs (**Table 5**), ethyl butyrate (apple), ethyl isovalerate (orange), isoamyl acetate (banana), ethyl hexanoate (green apple) and 2-phenylethyl acetate (flowers) should be considered as important contributors to the typical aroma of Malvasia wines. In the case of M6 no differences were found on any of the esters studied so we can conclude that maceration for a reduced period of time has not affected the ester content of the resulting wines.

Eight terpenes were identified in the wines, among them, linalool, β-citronelol and geraniol increased significantly with M18 while with M6 only β-citronelol increased significantly. Ninety percent of geraniol is in the skins, while linalool is distributed 50% between the skin and 50% in the pulp [33, 34]. Other authors [35] reported high concentrations of geraniol and its derived products throughout the ripening process in Malvasia grapes. Only linalool reached concentrations above its odor threshold in all wines, with the highest significant extraction in M18 wines.


*Influence of Skin-Contact Treatment on Aroma Profile of Malvasia* Aromatica *Wines… DOI: http://dx.doi.org/10.5772/intechopen.99216*

*\* OTH: Odor threshold values.*

*a OAV: Odor activity values calculated by dividing concentration by odor threshold value of the compound. OTH and OAV are given in mg l<sup>1</sup> except linalool and β-damascenone which are in μg l<sup>1</sup> . Sensory descriptor according to: <sup>b</sup> [25, 26]. c [27].*

#### **Table 5.**

*Odor threshold values and odor activity values of the volatile compounds with the greatest influence on the aroma of Malvasia wines from the two skin contact treatment (A1: C-M18; A2: C-M6).*

This terpene gives the wine floral and citrus notes (**Table 5**) typical of Muscat because it is one of the main compounds involved in the typical aromas of this variety [36]. Similar results were found by other authors in wines from white varieties for this family of compounds [23, 37].

β-damascenone was the only compound from the C13-norisoprenoid family found in Malvasia wines. The concentration of this compound decreases with skincontact time, showing a significant decrease in M18 wine. C13 come from the carotenoids degradation and the hydrolysis of their glycosylated forms. In young wines they are usually present in the form of glycoconjugates [38, 39]. According to the OAVs, in all wines β-damascenone is above its perception threshold and should be considered as an important compound in the aroma of Malvasia wines (**Table 5**). Provides floral aromas with lilac attributes [17]. Other authors agree with these results for this variety [40].

The most abundant fatty acids in the wines were hexanoic and octanoic acid (**Table 4**). These results are in agreement with those found by other authors [3, 41, 42]. The maceration seems to have different effects depending on the compound and the contact time between the skin and the must. In the case of M18 wines, the total concentration of fatty acids decreases, being particularly significant in octanoic acid. In M6 wines the total concentration of fatty acids increased significantly for hexanoic,

octanoic and decanoic acid regards to the conventional way. In all wines, regardless of the increase or decrease produced as a result of skin-contact, isovaleric, hexanoic and octanoic acids have OAVs >1 so must to be accounted in the aroma of Malvasia wines (**Table 5**). Regarding the group of aldehydes and ketones, it is known that alterations due to oxidation processes, imply the appearance of unpleasant aromas (cooked vegetables) related to the presence of compounds such as benzaldehyde, acetoin, hexanal, methional etc. [43]. Acetoin and benzaldehyde were detected in the control and M18 wines, with a significant increase in both with the maceration process (p < 0.05 and p < 0.001 respectively). According to [44] on the Verdejo grape variety, the presence of acetoin in white wines is considered negative for the flavor. In both cases, acetoin and benzaldehyde concentrations are below their perception threshold 150 mg/L [45] and 5 mg/L [46].

The two treatments (M18 and M6) significantly increased the concentration of γ-butyrolactone respect to the conventional way but in all cases it was far from its OTH (35 mg/L [47]).

## **3.4 Influence on sensory profile of wines**

Wines were evaluated using descriptive and preference tests. The olfactory phase of the Malvasia wines from assay 1 (A) and assay 2 (B) is shown in **Figure 2**. The macerated wine (a) 18 hours had a higher score in the descriptors of altered

#### **Figure 2.**

*Olfactory phase for the sensory analysis of the Malvasia wines from assay 1 (a) and assay 2 (b).*

*Influence of Skin-Contact Treatment on Aroma Profile of Malvasia* Aromatica *Wines… DOI: http://dx.doi.org/10.5772/intechopen.99216*

aroma due to problems during the conservation process of the M18 wine. Tasters also indicated oxidation aromas in M18 sample with a significance level of p < 0.001. The conventional wine in assay 1 was scored positively on overall aroma quality and fruity character (p < 0.01). In spite of the above-mentioned defects, the M18 wine received the highest score in floral character, being significantly superior to the control wine. This fact is in consonance with the results obtained in the aroma profile of these wines (see **Table 4**). In **Figure 2(b)**, M6 wines score higher in terms of fruit and floral aromatic intensity (p < 0.05). The rest of the parameters obtained similar scores regarding their control.

**Figure 3** contain graphs of the taste using different winemaking methods. The results of the taste evaluation of in assay 1 (a), show significant differences in favor of C wine in overall taste quality (p < 0.001), bitterness (p < 0.01) and fruity character (p < 0.01). This could be related to the oxidation suffered by the M18. In case of assay 2, M6 wine (b) received the highest score in the fruity character with respect to the control (p < 0.01). This fact may be related to the release of varietal aromas through the hydrolysis of aromatic precursors by the enzymatic activity over the period of conservation in the bottle.

In the preference test, in A1 the preferences were shared between the M18 and C wines. The most preferred wine was the one produced with a 6 h skin contact treatment in the A2.

#### **Figure 3.**

*Taste phase for the sensory analysis of the Malvasia wines from assay 1 (a) and assay 2 (b).*
